Study of Dynamic Behaviour of Viscoelastic Sandwich Materials. 2nd Report. Identification of Damping Properties of Sandwich Beam by Using Transfer Function Technique.

Abstract

A new identification method for the loss factor and Young's modulus of viscoelastic three-layered beams was studied. The test beam, composed of two surface sheets with viscoelastic resin between them, was excited at its center sinusoidally. Vibration velocity ω and force F0 were measured at the center, and frequency response curves of transfer function ω/F0 were obtained using a two-channel fast Fourier transform analyzer. The complex Young's modulus E(1+jη) of the three-layered beam was determined as ω/F0, whose measurement satisfies the beam equation of motion at every frequency. Good agreement was achieved for the complex Young's modulus measured by this method and by the conventional method. Shear modulus G'+jG" of viscoelastic resin was also calculated from the complex Young's modulus by means of the Ross-Kerwin-Ungar model. Good agreement was also obtained for the shear modulus. These agreements suggest that the new identification method presented is reliable enough to measure E(1+jη) of the three-layered beam and G'+jG" of viscoelastic resin in the middle layer.